Currently, SEEK_HOLE implementation in ext4 may both return that there's
a hole at some offset although that offset already has data and skip
some holes during a search for the next hole. The first problem is
demostrated by:
xfs_io -c "falloc 0 256k" -c "pwrite 0 56k" -c "seek -h 0" file
wrote 57344/57344 bytes at offset 0
56 KiB, 14 ops; 0.0000 sec (2.054 GiB/sec and 538461.5385 ops/sec)
Whence Result
HOLE 0
Where we can see that SEEK_HOLE wrongly returned offset 0 as containing
a hole although we have written data there. The second problem can be
demonstrated by:
xfs_io -c "falloc 0 256k" -c "pwrite 0 56k" -c "pwrite 128k 8k"
-c "seek -h 0" file
wrote 57344/57344 bytes at offset 0
56 KiB, 14 ops; 0.0000 sec (1.978 GiB/sec and 518518.5185 ops/sec)
wrote 8192/8192 bytes at offset 131072
8 KiB, 2 ops; 0.0000 sec (2 GiB/sec and 500000.0000 ops/sec)
Whence Result
HOLE 139264
Where we can see that hole at offsets 56k..128k has been ignored by the
SEEK_HOLE call.
The underlying problem is in the ext4_find_unwritten_pgoff()
implementation which in some cases fails to update returned offset when it
finds a hole and in some cases the condition for detecting a hole is
just wrong.
Fix ext4_find_unwritten_pgoff() to always properly update returned
offset and detect a hole.
CC: stable@xxxxxxxxxxxxxxx
Fixes: c8c0df241cc2719b1262e627f999638411934f60
CC: Zheng Liu <wenqing.lz@xxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/ext4/file.c | 25 +++++++++----------------
1 file changed, 9 insertions(+), 16 deletions(-)
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 831fd6beebf0..e4de6769376b 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -486,29 +486,18 @@ static int ext4_find_unwritten_pgoff(struct inode *inode,
(pgoff_t)num);
if (nr_pages == 0) {
if (whence == SEEK_DATA)
- break;
+ goto out;
BUG_ON(whence != SEEK_HOLE);
- /*
- * If this is the first time to go into the loop and
- * offset is not beyond the end offset, it will be a
- * hole at this offset
- */
- if (lastoff == startoff || lastoff < endoff)
- found = 1;
break;
}
/*
- * If this is the first time to go into the loop and
- * offset is smaller than the first page offset, it will be a
- * hole at this offset.
+ * If current offset is smaller than the first page offset,
+ * there is a hole at this offset.
*/
- if (lastoff == startoff && whence == SEEK_HOLE &&
- lastoff < page_offset(pvec.pages[0])) {
- found = 1;
+ if (whence == SEEK_HOLE && lastoff < page_offset(pvec.pages[0]))
break;
- }
for (i = 0; i < nr_pages; i++) {
struct page *page = pvec.pages[i];
@@ -571,13 +560,17 @@ static int ext4_find_unwritten_pgoff(struct inode *inode,
if (nr_pages < num && whence == SEEK_HOLE) {
found = 1;
*offset = lastoff;
- break;
+ goto out;
}
index = pvec.pages[i - 1]->index + 1;
pagevec_release(&pvec);
} while (index <= end);
+ if (whence == SEEK_HOLE && lastoff < endoff) {
+ found = 1;
+ *offset = lastoff;
+ }
out:
pagevec_release(&pvec);
return found;
--
2.12.0
